Some comments on gamma-ray implant dosimetry

Dosimetry calculations were made on the basis of recent photon interaction data and compared with existing sources. The build-up effect in muscle, photon attenuation in the source, filtration medium, and muscle, and 12 principal photon lines were incorporated in the calculations, and radium seeds of two standard dimensions were used. The results were within 1% agreement with previous findings for a 1-mCi radium source but showed an apparent discrepancy for a 13.3-mCi radium source filtered through a platinum tube, due to photon attenuation and scatter. These results may be extrapolated to fit circumstances such as drug-impregnated tissue.

Isolation and characterization of three unusual membrane glycopeptides present in rat intestinal endoplasmic reticula

Three glycopeptides have been isolated from the mucosal homogenates of the rat small intestine without using proteolysis. These glycopeptides appear to be localized exclusively in the membranes of the endoplasmic reticula. Although they have similar molecular weights of about 2550 and have similar amino acid compositions, they differ in the carbohydrate constituents. The major glycopeptide has 2 mol glucose per polypeptide chain while the two other glycopeptides contain 1 mol fucose, mannose and galactose with either 1 or 2 mol glucose. No hexosamine or sialic acid was detected in any of the glycopeptides. An unusual physical property was found associated with these glycopeptides. Below pH 6.5 they formed a precipitate which prevented them from diffusing through a dialysis membrane and allowed them to be rapidly purified following solubilization from the membrane. These glycopeptides appear to represent a new group of heretofore uncharacterized membrane constitutents which may play a role in some function specific for the endoplasmic reticula.

Rat intestinal brush border membrane peptidases. II. Enzymatic properties, immunochemistry, and interactions with lectins of two different forms of the enzyme

The properties of two purified peptidases derived from the intestinal brush border membrane of the rat have been investigated. The pH optima, heat stabilities, substrate specificities, and metal ion requirements of the two enzymes and the effects of inhibitors on their activities were nearly identical. The isoenzymes catalyzed the hydrolysis of a wide range of peptides containing from 2 to 8 amino acid residues. The enzymes are aminopeptidases; no evidence for carboxypeptidase or endopeptidase activity was found. For hydrolysis, there appears to be an absolute requirement for an L-amino acid at the NH2-terminus of the peptide substrate. There was a similar but less absolute requirement for the penultimate NH2-terminal amino acid. Thus, although peptides of the type L-aminoacyl-L-proline, L-aminoacyl-L-prolyl-(L-amino acid)n, or L-aminoacyl-D-amino acid were not hydrolyzed, L-leucyl-beta-naphthylamide could be utilized as a substrate. The enzymes appeared to be metalloenzymes in that metal ion-chelating agents could inhibit their activities. Co2+ partially restored the activities lost by chelation. Immunodiffusion studies showed that the two enzymes were immunologically identical. The antipeptidase antisera were specific for the enzymes and did not react with other constituents of the intestinal cell. Both enzymes have binding sites for the lectin phytohemagglutinin which recognizes N-acetylgalactosamine residues located at or near the terminal positions of glycoprotein carbohydrate chains. Both the lectin and the antibodies inhibited enzyme activities, but the mechanisms of inhibition appeared to be different.

Rat intestinal brush border membrane peptidases. I. Solubilization, purification, and physicochemical properties of two different forms of the enzyme

Two brush border peptidases have been isolated from the particulate fraction of the rat intestinal mucosa and purified to homogeneity as judged by polyacrylamide gel electrophoresis, starch gel electrophoresis, isoelectric focusing, and double immunodiffusion. For convenience, the peptidases have been designated peptidase F (fast) and S (slow) on the basis of their anodic mobilities. The isoelectric point of peptidase F was 4.76 and of peptidase S, 5.10. Both enzymes are glycoproteins. The amino acid compositions of the two peptidases are similar. The same carbohydrates are found in both enzymes, but there are differences in the molar concentrations of individual sugars. Peptidase S has greater concentrations of mannose and galactose and of hexosamines than peptidase F, while sialic acid is slightly greater in peptidase F. Carbohydrate accounted for approximately 19% and 23% of the weight of peptidases F and S, respectively. Estimates of the molecular weights of both enzymes by gel filtration gave values of 280,000. Electrophoresis of the enzymes under denaturing conditions on sodium dodecyl sulfate polyacrylamide gels indicated that each enzyme is a dimer consisting of two subunits of equal molecular weight, 140,000.

Release of peptide hydrolases during incubation of intact intestinal segments in vitro

1. Rat intestinal segments have been incubated in isotonic saline in vitro and release of peptide hydrolase enzymes into the incubation media examined over a 90 min study period. 2. Chemical assay data, as well as analysis of electrophoretic mobilities of release enzymes on starch gel, indicate that peptide hydrolase enzymes in the incubation media originate predominantly from the cytoplasm of the mucosal cells. 3. Peptide hydrolases were released rapidly from intact intestinal segments. Release occurred from the start of the in vitro incubations and was not affected by temperature and shaking. 4. It is concluded that compared to the in vivo situation, cytoplasmic peptide hydrolases are released from intestinal tissue very rapidly in vitro. Caution is therefore required when comparing results of in vivo and in vitro peptide absorption experiments.

Oxalate, calcium uptake and ATPase activity of sarcoplasmic reticulum vesicles

Ca++-uptake and Mg++-Ca++-dependent ATPase activity of skeletal muscle sarcoplasmic reticulum vesicles were reciprocally affected by increasing the oxalate concentration from 0 to 4 mM. At 0-0.1 mM oxalate approximately 17% of the calcium was removed by the vesicles from the medium while the ATPase activity was maximal (approximately 0.66 mumoles Pi mg-1 protein min-1). Between 0.1 to 0.2 mM oxalate the ATPase activity was reduced to one-fifth but the uptake rose sharply and 100% of the 45Ca++ was removed from the medium. The uptake was maintained at this level at oxalate concentrations greater than 0.4 mM but the ATPase activity remained inhibited. The kinetics of Ca++-uptake and ATPase activity were also differentially affected by oxalate. In the presence of oxalate, ruthenium red had only a very slight inhibitory effect on the calcium uptake. Addition of 0.1 mM EGTA removed 80% of the Ca++ from preloaded vesicles within 10 min. The formation of insoluble Ca-oxalate salt on the surface of the vesicle is suggested by these results. Calculations based on the Ksp of the calcium oxalate salt are presented to show its formation and the possible speciation of a Ca-oxalate complex which may affect the Ca++-uptake and ATPase activity.

Short chain fatty acids in rats with jejunal blind loops. I. Analysis of SCFA in small intestine, cecum, feces, and plasma

The luminal and plasma levels of short chain fatty acids (SCFA), products of bacterial fermentation, were measured in rats with surgically produced, self-filling blind loops located in the proximal small intestine. High levels of acetic, propionic, and butyric acids were detected in the blind loop segment and in the distal small bowel, regions which in normal and sham-operated rats contain no SCFA. Isobutyric, isovaleric, and valeric acids were also present. Feeding or fasting made little difference in the amount or composition of luminal SCFA. Although the amount of SCFA in each animal varied, the ratio of these acids was relatively constant. The ceca of the blind loop rats had relatively less acetic acid (48% of total SCFA) than did normal rats (64%) and proportionately more isobutryic, isovaleric, and valeric acids. The concentrations of SCFA increased in the feces of blind loop rats. The acetic acid concentration was 50% higher in blind loop rat feces; propionic, isobutryic, and isovaleric acids were elevated to a greater extent. The total output of most of the SCFA was also of acetic acid (137 +/- 32 mug per ml), the rest being isovaleric (5.2 +/- 2.6 mug per ml) and isobutyric (1.4 +/- 0.7 mug per ml) acids. Blind loop animals had nearly twice the concentration of acetic acid in the plasma (240 +/- 29 mug per ml) as normal animals, while the other acids were unchanged. The present study suggests that endogenous substances may be important substrates for the production of SCFA in the intestinal lumen. The high levels of SCFA in the small intestine and in feces and the substantial increase in the concentration of acetic acid in thvergrowth syndrome if the same relationships were found in man.

A study of intraluminal peptide hydrolase activity in the rat

1. Uncentrifuged and centrifuged rat intestinal contents were assayed for peptide hydrolase activity with glycyl-L-phenylalanine (Gly-Phe) and L-phenylalanyl-glycine (Phe-Gly) as substrates in the absence and presence of the intestinal cytosol peptide hydrolase inhibitor p-hydroxymercuribenzoate. 2. Jejunal contents hydrolysed Gly-Phe faster than Phe-Gly. Conversely, ileal contents hydrolysed Phe-Gly faster than Gly-Phe. 3. p-Hydroxymercuribenzoate markedly inhibited jejunal peptide hydrolase activity. There was ten times as much PHMB-resistant activity towards both dipeptides in ileal contents as in jejunal contents. 4. Most of the luminal enzyme activity was present in the supernatants after centrifugation, indicating the luminal enzymes exist in the soluble form. Although the presence of soluble bacterial enzymes cannot be excluded, peptide hydrolase enzymes in jejunal contents have the characteristics of mucosal cytosol enzymes whereas enzymes in ileal contents have the characteristics of mucosal bruch border as well as cytosol enzymes.

Glycoprotein metabolism in inflammatory and neoplastic diseases of the human colon

Carbohydrate compositions of the membrane and cytoplasmic fractions of human normal and cancerous colonic mucosa were compared in patients with blood groups O and B. The total sugar content in both fractions was reduced in the cancer tissues to about one-third of that in the normal colonic mucosa. The sugars that are associated with mucinous glycoproteins such as fucose and N-acetylgalactosamine were reduced significantly, while sugars that are primarily associated with "serum-type" glycoproteins were relatively unchanged or reduced to a lesser extent. The activities of glycoprotein:glycosyltransferases were variable, some showing so significant change, others beinb significnatly reduced in cancerous tissues. A polypeptidyl:N-acetylgalactosaminyltransferase (an enzyme that catalyzes the transfer of the first sugar to hydroxyamino acids of the protein core of mucinous glycoproteins), a sialyltransferase (involved in the addition of sialic acid to mucinous glycoproteins), and a galactoxyltransferase (thought to be responsible for blood group B antigenicity) were reduced in the cancerous colonic tissue. In contrast, the activities of these glycosyltransferases were unchanged in the colonic mucosa of patients with granulomatosis or ulcerative colitis. Glycosidase activities in the normal, cancerous, and inflammatory tissues were the same. These results suggest that in colonic cancer tissues the synthesis of one type of oligosaccharide chain may be greatly affected, while another family of oligosaccharides may remain relatively unaffected.

Studies on the binding of amylopectin sulfate with gastric mucin

Amylopectin sulfate, a sulfated polysaccharide that has an antipeptic property, was examined for its ability to bind gastric mucins. After chemically cross-linking the amylopectin sulfate into an insoluble gel, its binding with mucins isolated from antral and fundic mucosa of canine stomachs was studied with chromatography. A component present in both mucin fractions bound to the amylopectin sulfate gel below pH 4.5. This binding was reversible, and the complex dissociated above pH 5. Similar binding properties were found with soluble amylopectin sulfate. The component of the mucine which bound to amylopectin sulfate differed from the one which did not bind in its electrophoretic mobility and in its higher proportion of basic amino acids and a lower hexosamine, serine, and threonine content. This study suggests that amylopectin sulfate may bind to gastric mucins only under conditions of low pH.

Regional and cellular localization of glycosyltransferases in rat small intestine. Changes in enzymes with differentiation of intestinal epithelial cells

Optimal assay conditions were determined for four glycosyltransferases in rat small intestinal mucosal homogenates and the regional distribution and cellular localization of these enzymes was studied. For each glycosyltransferase, similar levels of activity were found in duodenal, proximal jejunal and distal ileal segments; activities of the galactosyltransferases were lower in the distal jejunal-proximal ileal segment. Planar section studies indicated that the undifferentiated crypt cells had significantly higher levels of sialyltransferase activities in the jejunum and ileum than the mature villus cells. A similar crypt to villus gradient was found for a galactosyltransferase in the ileum. These data suggest that glycoprotein synthesis may be active in the undifferentiated crypt cells and that certain glycosyltransferases may serve as marker enzymes for cellular differentiation in the intestine.

Glucocorticoid inhibition of protein synthesis in vivo and in vitro

In young adult rats receiving glucocorticoids in pharmacological amounts, the accumulation proteins in the liver was suppressed. In vivo pulse-labeling experiments showed that inhibition of protein synthesis in the liver was an early effect of a single dose of glucocorticoid followed by a stimulation of protein synthesis. In animals receiving multiple doses of glucocorticoid over a period of a few days, a more pronounced inhibition in protein synthesis was observed, and the secondary stimulation of protein synthesis did not occur. These in vivo observations were paralleled by the results with cell-free protein-synthesizing systems, which indicated that the glucocorticoid inhibitory effect was imparted to the soluble fraction of the liver.

Differential binding to Sepharose-Con A of B12-binding proteins from human gastric juice

Human gastric juice was found to contain at least two vitamin B-12 binding substances. One of the proteins which formed a complex with B12 was found to bind to a column containing Sepharose-ConA. Since the protein which bound to Sepharose-ConA was absent in the gastric juice of pernicious anemia patients it was concluded that this protein was intrinsic factor. The ability of intrinsic factor to bind to Sepharose-ConA offers a potential means by which intrinsic factor could be separated from other B-12 binding proteins in gastric juice. The ConA binding properties of intrinsic factor might be exploited in the development of a diagnostic test for pernicious anemia.

Alterations of membrane glycopeptides in human colonic adenocarcinoma

Membrane glycopeptides were examined in human colonic adenocarcinoma and normal colonic mucosa. The carbohydrates of membrane glycopeptides were found to be markedly reduced in tumor tissue and the relative proportions of the various sugars were altered. Although all of the sugars were lower in tumor tissue when compared to the adjacent normal mucosa, galactosamine, fucose, and sialic acid were more significantly reduced. Examination of the blood group activity and lectin-binding properties of membrane glycopeptides revealed that specific carbohydrate structures had changed in the tumor tissue. Most striking of these changes was the disappearance of glycoprotein-associated blood group A activity. Assay of the enzyme responsible for synthesis of the blood group A determinant showed that this glycosyltransferase activity was greatly diminished in tumor tissue. A galactosyltransferase and a fucosyltransferase were also significantly lower in the tumor tissue whereas the levels of another galactosyltransferase and a sialyltransferase were unaltered. Glycosidase activities in the normal and tumor tissues were similar. The results show that an alteration in glycoprotein biosynthesis occurred during tumorigenesis that resulted in a modified membrane glycoprotein composition and that these changes are probably a reflection of reduced levels of the enzymes responsible for glycoprotein synthesis.

The responses of rat intestinal brush border and cytosol peptide hydrolase activities to variation in dietary protein content: dietary regulation of intestinal peptide hydrolases

The effects of variation in dietary protein content on small intestinal brush border and cytosol peptide hydrolase activities have been investigated. One group of rats was fed a high protein diet (55% casein) and another group was fed a low protein diet (10% casein). After 1 wk, brush border peptide hydrolase activity (L-leucyl-beta-naphthylamide as substrate) and cytosol peptide hydrolase activity (L-prolyl-L-leucine as substrate) were determined in mucosae taken from the proximal, middle, and distal small intestine. As judged by several parameters, brush border peptide hydrolase activity was significantly greater in rats fed the high protein diet when data for corresponding segments were compared. In contrast, no significant difference was seen in cytosol peptide hydrolase activity. IN A SECOND STUDY, BRUSH BORDER AND CYTOSOL PEPTIDE HYDROLASE ACTIVITIES WERE DETERMINED IN THE PROXIMAL INTESTINE BY UTILIZING AN ADDITIONAL THREE PEPTIDE SUBSTRATES: L-leucyl-L-alanine, L-phenylalanylglycine, and glycyl-L-phenylalanine. Sucrase, maltase, and alkaline phosphatase activities were also determined. As before, brush border peptide hydrolase activities were significantly greater in rats fed the high protein diet. However, activities of the nonproteolytic brush border enzymes did not vary significantly with diet. In contrast to the results obtained with L-prolyl-L-leucine as substrate for the cytosol enzymes, cytosol activity against the three additional peptide substrates was greater in rats fed the high protein diet. It is suggested that the brush border peptide hydrolase response to variation in dietary protein content represents a functional adaptation analogous to the regulation of intestinal disaccharidases by dietary carbohydrates. The implication of the differential responses of the cytosol peptide hydrolases is uncertain, since little is known of the functional role of these nonorgan-specific enzymes.

Changes in sucrase, enterokinase, and peptide hydrolase after intestinal resection. The association of cellular hyperplasia and adaptation

In a study of changes in digestive enzymes after massive intestinal resection and the mechanisms by which such changes occur, rats were sacrified 4 wk after removal of the proximal two-thirds of the small intestine. Alterations in the mucosal levels of sucrase, enterokinase, and dipeptide hydrolase (L-leucyl-L-alanine substrate) were examined in the light of associated changes in protein. DNA and wet mucosal weight, measured in standardized gut segments from various regions of intestine. Metabolic studies showed that normal growth patterns were reestablished after the operation but significant elevations in stool weight and fecal nitrogen occurred in the second postoperative week, falling towards normal by the 4th wk. In standard gut segments wet weight of mucosa, protein, and DNA rose, especially in distal segments, DNA increasing disproportionately. Mucosal levels of the proximally distributed and membrane-bound enzymes, sucrase and enterokinase, showed similar patterns of change: when enzyme activity was expressed in terms of the total per segment, proximally there were considerable increases in both enzymes, but, expressed in terms of specific activity, that of sucrase fell and that of enterokinase was unaltered. By contrast, the largely soluble and more distally distributed dipeptide hydrolase increased more in distal segments and the increases in total activity were accompanied by lesser increases in specific activity. However, in spite of increases in total activity, enzyme activity per milligram DNA fell by over 50% in postanastomotic segments. Subcellular distribution studies showed no change in the percentage of the total activity which was membrane-bound and zymograms confirmed that no new dipeptide hydrolase had appeared after resection. It is concluded that increases in the segmental totals of various enzymes seen after resection are achieved by disproportinate increases in the number of mucosal cells per segment and that the greatest change in a particular enzyme occurs in the region where the enzyme is normally found in highest concentration.

Glycosyltransferases in human blood.I. Galactosyltransferase in human serum and erythrocyte membranes

Human serum and hemoglobin-free erythrocyte membranes were found to contain a galactosyltransferase which catalyzes the transfer of galactose from UDP-galactose to specific large and small molecular weight acceptors. The requirements for enzyme activity were found to be similar for the enzymes from both sources. However, the membrane-bound enzyme depended on a detergent for maximal activity. Mn(++) was an absolute requirement for transfer and uridine nucleoside phosphates were inhibitors. The most effective acceptor for galactose was a glycoprotein containing N-acetylglucosamine residues in the terminal position of its oligosaccharide side chains, N-acetylglucosamine was also an acceptor. While the presence of alpha-lactalbumin in the incubation medium resulted in a significant decrease in the transfer of galactose to N-acetylglucosamine, glucose, which was not an acceptor for galactose in the absence of alpha-lactalbumin, became an excellent acceptor. The serum enzyme catalyzed the transfer of 54 nmoles of galactose per milliliter of serum per hour and its apparent K(m) for UDP-galactose was 7.5 x 10(-6)M. The membrane enzyme had a similar apparent K(m). Using a quantitative assay system the enzyme was found to be present in all individuals studied, regardless of their blood type, secretor status, or sex.

Glycosyltransferases in human blood. II. Study of serum galactosyltransferase and N-acetylgalactosaminyltransferase in patients with liver diseases

Serum galactosyltransferase activity was found to be elevated in patients with alcoholic and other liver disorders but remained at a normal level in patients with a variety of nonhepatic diseases. The properties of the galactosyltransferase in patients with liver disease were compared with those of the enzyme in the serum of normal subjects. The possible presence of inhibitors or activators in the serum was examined. Results indicated that in patients with liver disease, the rise in the serum galactosyltransferase was due to an increase in the level of the enzyme present in normal serum and not due to the appearance of a new enzyme. In the cases examined, the level of the enzyme increased with the deterioration of liver function and declined in a patient recovering from acute alcoholic hepatitis. Another glycosyltransferase, an N-acetylgalactosaminyltransferase, was not elevated in the serum of liver disease patients and, unlike the galactosyltransferase, was not detected in normal liver. The results suggest that the serum galactosyltransferase originates from the liver and that an abnormal rise in the level of this enzyme in serum is due to hepatocellular damage.

Peptide hydrolases in the bruch border and soluble fractions of small intestinal mucosa of rat and man

Peptide hydrolases, catalyzing the hydrolysis of 13 dipeptides and 5 tripeptides into their respective amino acids, were studied in small intestinal mucosa and other tissues, in man and in the rat. Studies on the subcellular distribution of these enzymes showed enzyme activities in both the soluble and brush border fractions of the rat small intestinal mucosa, the former constituting 80-90% and the latter 10-15% of the total activity. Zymogram studies of peptide hydrolases, in both fractions, yielded multiple bands indicating multiple zones of enzyme activity. With most substrates a rather broad range of enzyme activities was observed in the soluble fraction differing only slightly from substrate to substrate, the exception being when L-leucyl-L-proline was used: this latter led to a zymogram pattern which was quite distinct. The synthetic substrates, L-leucyl-beta-naphthylamide and L-leucinamide appeared to be hydrolyzed by two electrophoretically distinct enzymes, different from those hydrolyzing other leucyl-containing peptide substrates. Zymogram patterns of the brush border membrane fraction were quite different from those of the soluble fraction of rat small intestine indicating that enzymes from the two sources may be different. No comparable human data were obtained.Peptide hydrolases in the soluble fractions of various organs from the same species gave similar zymogram patterns, while those from the plasma membrane-bound fractions of different organs in the same species were peculiar to each organ. From these data, it is suggested that peptide hydrolases in the brush border and the soluble fractions of small intestine are distinct enzymes and may play different roles in cellular function.

Glycoprotein biosynthesis in small intestine. 3. Enzymatic basis for the difference in the antigenicity of mucins

Rat small intestinal mucosa was examined for ability to produce mucins with human blood group A, B, and H activity. Blood group activity of the mucins was compared to antigenic activity of red blood cells in individual rats and the enzymatic basis for differences was investigated. Red cells in all the rats examined contained human blood group A and B antigens. All rats synthesized intestinal mucins having B and H antigenic activity but 57% failed to produce mucins with blood group A activity (A(-)); the remaining 43% (A(+)) produced A substance. The activities of five glycosyltransferases including alpha(1-->2) fucosyltransferase, the determinant of human secretor status, were measured in the intestine of A(+) and A(-) rats. Four enzymes were the same in both groups, while the fifth, N-acetylgalactosaminyltransferase, was present only in A(+) rats. The specificity of this latter enzyme, as found in the rat, appeared similar to that in humans, since it catalyzed addition of N-acetyl-D-galactosamine only to acceptors which had the H determinant structure. In the presence of the enzyme, A(-) mucin could be converted to A(+) mucin; this was shown both by hemagglutination inhibition and immunoprecipitin studies of the products of incubation of A(-) mucin with UDP-N-acetyl-D-galactosamine and the enzyme. These studies indicate that the difference between A(+) and A(-) rats is due to the apparent absence of N-acetylgalactosaminyltransferase in the intestinal mucosa of A(-) rats. These rats may provide experimental models for studies on the effect of ABO and secretor status on susceptibility to ulceration and carcinogenesis.